The present invention relates generally to electronic circuits and, more particularly, to dual input differential amplifiers.
Current mixed mode signal processing techniques rely heavily on switched capacitor circuits because of the high levels of integration in metal-oxide semiconductor (xe2x80x9cMOSxe2x80x9d) process technologies. As a result, in almost all available applications, reducing power dissipation becomes a key priority. Among the known techniques to reduce power dissipation, a widely used technique involves the reuse of the operational amplifiers (xe2x80x9copampsxe2x80x9d) in two complementary phases of the clock within two different stages.
For example, every stage in a pipeline A/D converter has a sample phase and a hold/amplify phase. In this case, the opamp is needed only in the hold/amplify phase. Therefore, two stages in the pipeline can share the same opamp.
FIG. 1 is a schematic diagram of a prior art circuit including a shared opamp 100. Referring to FIG. 1, if the opamp 100 is shared among two different stages, switching of the inputs and outputs between the two stages is required. However, since the opamp inputs are charge conservation nodes, any extraneous charge injected in those nodes during the opening of the switches in one stage corrupts the operation of the other stage, introducing stage-to-stage correlation and non-linearities in a pipeline analog/digital (xe2x80x9cA/Dxe2x80x9d) converter using this shared opamp technique. Therefore, in order to switch such opamp inputs, any residual charge at the switched nodes must be avoided or minimized.
Several techniques have been developed to reduce or eliminate the residual charge injection from switches or the residual charge due to incomplete stage settling or finite opamp open loop gain. However, these techniques require extra phases of the clock to perform a reset operation at the opamp inputs and, therefore, appear to cause an overall slowdown of the speed of the stage.
Embodiments for a dual input differential amplifier are described. The dual sets differential amplifier includes multiple input devices forming at least two sets of differential inputs for an operational amplifier, and multiple switches within the operational amplifier, each switch being coupled to a corresponding input device to switch an active input set of the at least two sets in order to enable a reduction in residual charge associated with switching at an output of the corresponding switch.
Other features and advantages of the present invention will be apparent from the accompanying drawings, and from the detailed description, which follows below.